(RealSimple.com) -- You've managed to make it to spinning class (for the second time this week!), but as soon as the instructor starts the cooldown, you head for the door. Hold it right there. Turns out, stretching is just as important as getting on the bike in the first place.

Although countless studies have shown how beneficial exercise is for your body and mind (it may do everything from reducing the risk of some cancers to helping improve memory), less attention has been paid to flexibility.

But doctors and physical therapists agree that it's a vital part of keeping your body fit and able. "Flexibility is the third pillar of fitness, next to cardiovascular conditioning and strength training," says David Geier, the director of sports medicine at the Medical University of South Carolina, in Charleston, and a spokesperson for the American Orthopaedic Society for Sports Medicine.

In fact, flexibility can help your body reach its optimum fitness level, may play a role in injury prevention, and can even contribute to staving off conditions like arthritis and more serious illnesses.

Here's how it works: When you stretch a muscle, you lengthen the tendons, or muscle fibers, that attach it to the bone. "The longer these fibers are, the more you can increase the muscle in size when you do your strength training," says Geier. That means that a more flexible muscle has the potential to become a stronger muscle, too.

In turn, building strong muscle fibers may boost your metabolism and your fitness level. Flexible muscles also make everyday activities easier on your body and may decrease your risk of certain injuries.

Common behaviors, such as hunching over the computer, can shorten some muscles. That, along with the natural loss of muscle elasticity that occurs with aging, can set you up so any quick or awkward motion (lunging to catch a glass before it teeters off the table, for example) could stretch your muscles beyond their limit, resulting in a strain or a tear.

"Even if you're aerobically fit, it helps to be limber, too, so your body can easily adapt to physical stressors," says Margot Miller, a physical therapist in Duluth, Minnesota, and a spokesperson for the American Physical Therapy Association.

What's more, stretching may improve your circulation, increasing blood flow to your muscles. And having good circulation can help protect you against a host of illnesses, from diabetes to kidney disease.

Greater flexibility has even been linked to a lower risk of cardiovascular disease. A 2009 study in the "American Journal of Physiology" indicated that people age 40 and older who performed well on a sit-and-reach test (a seated forward bend that measures flexibility) had less stiffness in their arterial walls, an indicator of the risk for stroke and heart attack.

First off: How flexible do you need to be? Not as much as you might think. Sliding into a split may be a good late-night cocktail-party trick, but it's not necessary to living a healthy life.

The general rule of thumb is, you need to be as flexible as your lifestyle dictates, says Malachy McHugh, director of research at the Nicholas Institute of Sports Medicine and Athletic Trauma at Lenox Hill Hospital, in New York City. For example, in the world of sports, long-distance runners are known to be notoriously inflexible. But that's OK, because their bodies don't need a lot of flexibility to move forward in a relatively straight line, says McHugh. A gymnast, on the other hand, needs a lot of flexibility to be able to flip and tumble without injury.

The rest of us need a level of flexibility that's somewhere in the middle. To increase your flexibility, start with about 10 minutes of stretching a day, focusing on the major muscle groups: upper body (arms, shoulders, neck), back, and lower body (thighs, calves, ankles).

Then, depending on how you typically spend your time, focus on specific stretches for problem-prone areas. So if you're pretty much parked at a desk from nine to five, you'll want to give extra attention to your lower back and shoulders. If you're on the move -- picking up toddlers and bags of groceries, perhaps -- concentrate on your hamstrings and arms.

If you don't have 10 minutes a day to spare, stretching just a few times a week can be nearly as beneficial. In fact, that may be enough to help you stay supple once you've gotten there. A study published in the "Journal of Strength Conditioning and Research" found that after stretching every day for a month, participants who went on to stretch just two or three times a week maintained their degree of flexibility. Those who stopped stretching, however, lost about 7 percent of their hip range of motion within a month.

Of course, you may find that stretching becomes one of your favorite parts of the day. Since you need to focus on even, deep breathing while listening to your body, stretching is a great relaxation or even meditation break. "The more you do it, the more you will get out of it -- both physically and psychologically," says Geier. No word yet on whether we can say the same about chocolate or "The Real Housewives."

The ultimate daily stretch

Warm up your muscles before you begin with a short walk or some jumping jacks. For each move, breathe out as you stretch. "You want a slow, smooth, and controlled movement," says physical therapist Margot Miller.

As you ease into each stretch, you'll feel the muscles relax a bit -- that's due to increased blood flow. Only move to the point of resistance; the stretch should not hurt. Be careful not to bounce (sorry, Jane Fonda), which can cause tiny injuries to the muscles. Complete the whole sequence here, designed by Emmanuel Durand, head coach for the Cirque du Soleil show "O," in Las Vegas, and Angelique Janov, a certified Pilates instructor and a contortionist coach for "O." It should take about 10 minutes.

Especially helpful if you sit at a desk all day, need to work on your posture, or carry tension in your upper body.

1. Place your hands on the back of your head and gently push it forward with your chin tucked. Hold for five seconds.

2. Now place the heels of your hands on your chin, fingers pointing toward your ears. Gently push your head back. Hold for five seconds.

3. Rest your right hand on the top of your head and gently press your right ear toward your right shoulder. Hold for five seconds. Repeat on the other side.

4. Raise your arms and clasp your hands above your head; imagine lifting and lengthening your spine. As you bend to the left, release your hands. Grasp your right elbow with your left hand and pull it to the left. Hold for five seconds. Come back to the center and repeat on the right side.